I didn't make the comparison with Somalia in particular. Somalia is a talking point of certain people on the left when they critique libertarianism. I don't like using it as an example because it limits the case too much. Somalia is supposed to be like a libertarian system because it had virtually no government, but that isn't the real issue. It has to do with the entire world of developing countries, not just Somalia. While I agree that many of these countries have authoritarian governments and hence could not be called libertarian, they resemble a libertarian system in the one way which matters most when we're talking about economic prosperity: these governments do not provide services to their citizens. Services such as the following:
1. a public retirement system, 2. healthcare for the elderly (or for everyone), 3. safety nets for those who lose their jobs, 4. a minimum wage, 5. regulations on business to protect the environment and to curb other abuses, 6. a protected right to strike, 7. free K-12 education, and others.
In the United States, libertarians have opposed all of these things, and/or advocated scaling them way back. Not all self-identified libertarians. I'm talking about doctrinaire libertarians. I'm not going to get into a definitional argument about this, but if you read what the intellectuals of this movement say, and their party platform, it's quite extreme. Moderate conservatives and liberals can call themselves libertarians if they want, but just being sort of fiscally conservative and supporting the Second Amendment isn't really libertarian. The core of it is a belief in
minimalist government, not a government which is like 85% of what we have now.
The point of all of this is to look at the world around us, and ask the basic question: which countries supply services like the ones I listed above, and which do not? And how well off economically are the ones who do offer such services versus the ones who do not? The answer provides a staggering contrast; it isn't merely a general trend in favor of the one over the other. ALL governments which supply most/all of these kinds of services are at least in the upper third of countries in the world in terms of economic prosperity, most in the upper 10%:
https://en.wikipedia.org/wiki/List_of_countries_by_Human_Development_Index
While the ones who do not are farther down, most being in the crapper. It's interesting that you point out the fact that many developing countries have authoritarian government. What that proves is that "big government" is not the same thing as authoritarian government. Equating the two is another fallacy of libertarians.
Broadly, this world consists largely of countries with "big government" i.e. high taxes and lots of services provided by the government, and "small government" with low/minimal taxes and little in the way of services. The former are generally democracies, while the latter are generally dictatorships. The former are generally prosperous, while the latter are generally not.
Either way, democracy or dictatorship, it's clear when you look around the world that minimalist government doesn't work.
Even if you look within the United States, you can see that red states which offer fewer services are generally less prosperous than are blue states which offer more.
http://www.businessinsider.com/state-economy-ranking-q4-2015-2016-1/#12-new-york-40
All the arguments over theory aside, the empirical evidence simply does not support this bizarre American only ideology that we call libertarian. It cuts forcefully the other way.
Libertarians are great when it comes to individual liberty. When it comes to matters of economic prosperity, they're terrible. Doing what libertarians want will turn us into a developing country, where every state has an economy like West Virginia or Arkansas, or worse.